Support ends 24 months after the next service pack releases or at the
end of the product's support lifecycle, whichever comes first.

SP2 is the final Service Pack available for Server 2003. You will lose support when Server 2003 as a platform is no longer supported. It was released on 3/30/2005 so it has mainstream support until 3/30/2010. You will have to deal with the extended support restrictions through 3/30/2015.